Posted on July 5, 2023
One of the U.S. Army Corps of Engineers, Galveston District’s missions is maintaining the depths of more than 1,000 miles of shipping channels; 270 miles of deep draft and 750 miles of shallow draft channels.
A deep draft channel is more than 14 feet deep and a shallow draft is less than 14 feet. The deepest parts of the Houston Ship Channel are 45 to 53 feet deep.
Each year, erosion deposits new loose sand and sediment into the channel. To keep the channel navigable, the Galveston District oversees maintenance dredging by commercial dredge companies.
That means a lot of mapping to make sure dredge companies are paid for the quantity of dirt and sand removed.
The Galveston District contracts commercial dredge companies to remove 15-25 million cubic yards of sediment annually from Texas shipping channels. If placed on one city block, it would create a mountain 14,000 feet above sea level.
Sonja Zindars is one of the newest members of the Galveston District. She is the Northern Area Office Hydro-Survey Chief. The Northern Area includes 175 miles of deep draft channels and 325 miles of shallow draft channels including the Gulf Intracoastal Waterway from Port Arthur to Matagorda Bay.
The Northern Area includes the Houston Shipping Channel (HSC), a 54-mile-long deep draft waterway which extends from Bolivar Roads near Galveston, Texas, north through Galveston Bay to Houston. The HSC is the busiest port in the U.S. by commercial tonnage.
Zindars’ area of responsibility includes the HSC and there is constant dredging construction to maintain navigable waterways.
“Contract construction surveys consist of before and after dredging surveys – these will provide the amount of cubic yardage to be removed,” Zindars said.
Survey teams make a detailed map of the sea floor before a dredge operation to estimate the amount of material to be removed and after the dredge has completed work on the section to calculate and verify that the contract work was completed.
If the dredge material is deposited offshore a survey team will make a third map of the sand added to the ocean floor.
There are 30 employees throughout the Galveston District involved with hydro-surveying. This team includes supervisors and survey coordinators, team leaders, hydro-surveyors, vessel captains, data managers and data processors. There are four Hydrographic Survey sections across the district, which includes the entire length of the Texas Gulf coast.
On June 5, 2023, a survey technician and boat captain aboard the Galveston District survey vessel, Tanner II, conducted a post dredge survey on a section of Upper Galveston Bay in the HSC.
Jasper Schaer has been a Galveston District Hydrographic Survey Team and Technical Lead for six months and a Galveston District employee for the last year. He has a Bachelor of Science degree in geology and practical work experience in surveying.
“Part of our contract is to do an after-dredge evaluation using single beam echo sounder and we do cross sections where they’ll calculate the volume and make sure that it met the contract and then the dredge company can be paid,” Schaer said.
Schaer manages all aspects of data collection during the mapping mission and helps the vessel captain when launching the watercraft and tying the boat up upon return to the Galveston District harbor.
Hydrography is very technical work; Schaer loads map templates into the ship’s computers for the specified work area to create a “before” picture, calibrates the sonar equipment for exact measurements of the channel floor and delivers the completed survey to the section’s data managers and data processors.
The transducer on the echosounder that is used to map the channel sends a sound wave through the water column, once it reaches the bottom the sound returns to the vessel’s receiver. The time it takes to send and receive the sound wave calculates the depth of the channel. While mapping the channel Schaer uses a sound velocity profiler to determine how fast the sonar wave passes through the water. The speed at which sound passes through the water is dependent on the temperature, salinity, and depth of the water. The sound velocity profiler measures these attributes as it travels through the water column. This data is then applied to the echosounder data to correct for the travel time of sound to the bottom and back.
James Hiroms piloted the Tanner II for the mission. Hiroms has been a Galveston District vessel captain since the year after he retired from the Coast Guard, Houston-Galveston sector, in 2016.
Hiroms has the challenging task of monitoring other boat and ship traffic in the busy Houston Shipping Channel as Schaer monitors the sonar and mapping equipment.
“This is a high traffic area, so of course, you have to have your head on a pivot,” Hiroms said.
During the survey, the team stopped the Tanner II many times to wait for large container ships or oil tankers to pass by the post dredge survey area.
Big ships throw off big wakes which can stir up the channel floor, including fine sediments known as “fluff”. The passage of a big ship means Schaer must take another sounding measurement due to additional suspended sediment to ensure the accuracy of the map.
The Derrick Barge or DB Avalon performed the dredging work for the section Schaer mapped. The DB Avalon is reportedly the largest clamshell dredge operating in North America, with a 30 cubic yard (198,000 pound) capacity clamshell bucket. The DB Avalon can move a bucket load every 1-2 minutes.
Previous dredge operations by the DB Avalon provided beneficial use of dredge material to the Dollar Reef oyster mitigation site.
Hiroms, a Corpus Christi native, has worked aboard the Tanner II for 7 years. He enjoys the day-to-day survey mission.
“Every day offers a new challenge, that’s the best part about it; every day the wind’s different, the current’s different, the traffic’s different; I just enjoy being on the water and every day [is] a new challenge,” Hiroms said.
“It’s very rewarding; my office is the ocean and we’re always looking for people who want to come along and come survey with us,” Schaer said.
For people interested in joining a survey crew, experience and training can be developed from within the survey group or from actual education within a hydrographic course of instruction. Texas A&M Corpus Christi has a newly developed program specializing in hydro-surveying.